So-called vertically-disposed engines each including a crankshaft disposed vertically are known from Japanese Patent Application Laid-open Nos. 63-192918 and 4-337143, in which a balancer shaft is supported on the side of a crankcase (on the side opposite from the cylinder block with the crankshaft interposed therebetween).
In the vertically-disposed engine described in the above Japanese Patent Application Laid-open No. 4-337143, the crankshaft is clamped between dividing surfaces of the cylinder block and the crankcase. However, such an engine suffers from a problem that if the balancer shaft is supported on the side of the crankcase, a bolt for coupling the crankcase to the cylinder block interferes with the balancer shaft and for this reason, a limitation is produced in the layout of the bolt and balancer shaft. Especially, when the balancer shaft is longer in the axial direction of the crankshaft, the above problem is significant, and it is difficult to dispose the balancer shaft without bringing about an increase in size of the crankcase.
An engine for an outboard engine system with a crankshaft disposed vertically is known from the above Japanese Patent Application Laid-open No. 4-337143, which includes a pair of secondary balancer shafts. In addition, an engine for an outboard engine system with a crankshaft disposed vertically is known from Japanese Utility Model Application Laid-open No. 3-76799, which includes an engine hanger on an upper surface of a cylinder block.
In the engine described in the above Japanese Patent Application Laid-open No. 4-337143, the pair of secondary balancer shafts are supported in the crankcase coupled to a front surface of the cylinder block. For this reason, if an attempt is made to ensure a space for disposition of the secondary balancer shafts, there is a possibility that the crankcase may protrude forwards (namely, toward a hull), thereby hindering the layout of auxiliaries around the crankcase. The art described in the above Japanese Utility Model Application Laid-open No. 3-76799 includes no balancer shaft and hence, the relationship between the engine hanger and a balancer shaft is not described.